Straw man. No one is claiming they aren't more complicated, but food intake is cornerstone, the foundation to understanding weight and weight loss. The complexity and nuance should be layered on top of this. Many ignore the foundation. See my other comments in this thread.
>mice fed a HFD-CysF diet were able to lose approximately 30% body weight within 1 week despite maintaining a high calorie intake
Maybe things are more complicated than just conservation of mass.